In general, the operating mechanism for a high-voltage switchgear is operated by opening/closing operation (interruption/closure operation) of the switchgear, by reciprocating drive of an electrical contact of the switchgear between the open and closed positions. In order for the switchgear to exhibit good interruption performance, it is important for the moving body including the electrical contact to be driven at high speed by the operating mechanism.
In this process, it is desirable for the operating mechanism to maintain the speed of the moving body until a little before it reaches the end position of its interruption operation and then to reduce the speed of the moving body in a comparatively short distance. Consequently, usually, a buffering device constituting means for reducing the speed of the moving body is employed in the operating mechanism.
A first prior art example of such a buffering device is disclosed for example in Laid-open Japanese Patent Gazette, Laid-open Patent Application Number H9-303,467 (FIG. 1) (hereinafter referred to as Patent Reference 1) or, likewise, Laid-open Japanese Patent Gazette, Laid-open Patent Application Number 2008-291898 (FIG. 1) (hereinafter referred to as Patent Reference 2). In this first prior art example, a double-layer cylinder comprising outer and internal cylinders is provided. Of these, the operating fluid is sealed within the external cylinder. Also, buffer orifices are formed at both ends of the internal cylinder.
In addition, within the internal cylinder, a slide rod and piston are slidably arranged. The slide rod is coupled with the drive section of an operating mechanism. Steps provided with a taper are arranged on both sides of the piston. The steps at both ends of the piston are fitted into the buffer orifices at both ends of the internal cylinder.
On the outside of the buffer orifices, a packing is arranged constituting a sealing section for preventing leakage of operating fluid that is sealed within the external cylinder. It should be noted that the operating fluid that flows out from the buffer orifices flows into the opposite side of the piston through an oil return passage that is formed from the gap between the external cylinder and the internal cylinder.
In a buffering device constructed as above, in the case of both interruption operation and closure operation, a slide rod (including a piston) that is coupled with the drive section of the operating mechanism is operated, and, just before the termination of operation, the steps of the piston penetrate into the buffer orifices. From this instant, the pressure within the buffer orifices rises, and a large reaction i.e. braking force is generated tending to push the piston back. By means of this braking force, it is possible to reduce the speed of the slide rod only just before termination of operation.
Also, a second prior art example of a buffering device for the operating mechanism for a switchgear is disclosed in Japanese Laid-open Patent Gazette, Laid-open Patent Application Number H 10-228847 (FIG. 1) (hereinafter referred to as Patent Reference 3). In this Patent Reference 3, just as in the above first prior art example, a double-layer cylinder is provided and a piston is freely slidably arranged in the interior of the internal cylinder. Also, in the internal cylinder, there are formed a plurality of outflow holes for operating fluid, along the circumferential direction. It should be noted that the piston is directly coupled with the output shaft of the operating mechanism.
In the above second prior art example, the number of outflow holes that are in an open condition decreases with sliding movement of the piston. Consequently, the rate of flow of operating fluid out from the internal cylinder decreases, with the result that the pressure of the operating fluid rises, generating braking force. Consequently, a large braking force is generated immediately prior to completion of operation, in reciprocal operation.